1. Field of the Invention
The present invention relates to apparatus and methods for testing welds and, more particularly, for testing welds on nozzles or other such fixtures. In one particular aspect, the invention is suited for testing welds while simultaneously applying an axial stress within the nozzle.
2. Description of the Prior Art
In chemical or petrochemical plants etc., it is often necessary to convey fluidic materials from one location, or holding cell to another. The conveyance of such material normally includes equipment such as conduits or pipes, storage or reaction vessels etc., which are generally manufactured from metal. The joining of separate pieces of the conveying equipment is generally achieved by welding the necessary pieces together. For example, when joining adjacent ends of pipe together, it is common for each end to be provided with flanges, welded to each respective end, which are then bolted together to form a seal. Alternatively, the ends of pipes or other equipment may be welded directly together for form the necessary conduit. In either case, it will be appreciated that each welded joint must form a complete seal so as to prevent leakage of the materials being transported. This is particularly the case when handling potentially hazardous (i.e. flammable) or toxic materials.
For reasons of safety, it is often necessary to periodically test the integrity of the welds used in joining the various pieces of equipment (such as pipes, vessels, flanges and the like) together. However, a particular problem is encountered when attempting to test the integrity of welds used in joining a nozzle to a pipe or vessel. Nozzles generally comprise a short conduit with one end inserted into or abutting an opening in a pipe or vessel and an opposite end having a flange. The joints between the conduit portion of the nozzle and the pipe or vessel and the flange, respectively, are sealed with welds. As is known in the art, nozzles can range in size from less than an inch to up to several feet in diameter.
The prior art teaches various tools for conducting weld integrity tests on conduits. For example, U.S. Pat. Nos. 6,131,441 and 5,844,127 (Berube and Carson) (the entire disclosures of which are incorporated herein by reference) teach weld testing tools which isolate a particular section of a pipe (for example, a section including a weld) and subject the section to a high pressure fluid within a constrained annular space defined by the tool and the inner surface of the pipe. The pressure of the fluid within the annular space is monitored whereby any pressure drop signifies a leak in the weld.
U.S. Pat. No. 6,463,791 (Berube and Carson) (the entire disclosure of which is incorporated herein by reference) teaches an apparatus for testing welds used to secure nozzles. As shown in FIG. 1 of this reference, the apparatus comprises a first seal plate that is placed on the inner surface of the vessel (for example) and a second seal plate that is secured to the outer, flange portion (i.e. the flange face) of the nozzle. The seal plates are connected to each other and the seals are formed by urging one against the other. In this manner, the nozzle volume is sealed and a pressurizing fluid is introduced therein. As will be understood, the process of urging the plates towards each other causes an axial compressive force to be applied on the flange and hence the welds provided on the nozzle.
Although the above-described references provide efficient tools for testing welds, they are designed to apply mainly a radial force against the weld. However, there exists a need for exerting further stresses on welds for providing a “worst case scenario” so that such welds can be tested under extreme conditions. More particularly, there exists a need to conduct weld tests while applying an axial expansion force on the welds being tested.